ES2986121T3 - Procedure for controlling a wind power installation - Google Patents

Abstract

The invention relates to a method for controlling a wind power plant (100) for supplying electric power to an electric supply network (120), and the wind power plant (100) comprises a tower (102) having a nacelle (104) rotatably arranged thereon; an aerodynamic rotor (106), which is drivable by the wind; a generator (302), coupled to the aerodynamic rotor (106), for generating electric power from the wind; a power unit (310) for driving the generator (302) to control an output of electric power from the generator (302) and/or to control a torque of the generator and a supply unit (101) for supplying the output of electric power from the generator (302) or part thereof to the electric supply network (120); and the method comprises the steps of controlling the wind power plant (100) such that, during normal operation, depending on the wind, an electrical supply power is supplied to the electrical supply network (120), the electrical supply power being modified according to a network state (fN) and/or a network demand (ΔPS) of the electrical supply network (120), wherein the modification of the electrical supply power is guided in such a way that a definable, mechanical, in particular instantaneous, load limit of the wind power plant (100) is maintained. (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Procedure for controlling a wind power installation

The present invention relates to a method for controlling a wind power installation. The present invention also relates to a wind power installation. The present invention also relates to a wind farm with a plurality of wind power installations.

Wind power plants are known to generate electrical power from the wind and feed it into a power supply network. This means that wind power plants can contribute to the supply of energy, but are also increasingly used to support the power supply network. It is particularly important to note that wind power plants are one of the fastest to regulate of all the generators they supply. This means that they can be used especially for quick and short-term changes in the power supply.

These good properties of wind power plants are becoming increasingly recognised and they are increasingly being used to back up or support the grid. In addition to the suitability of fast control of wind power plants, wind power plants can perform such supporting tasks, in particular a rapid increase or decrease of power, but not at any level and/or within a short time. It is particularly important to note that wind power plants can only supply the power grid with as much power permanently, i.e. if no corresponding storage is assigned to them, as is possible depending on the prevailing wind and of course the design of the wind power plant.

For this reason, it is known how to operate wind power plants with voluntary throttling, in order to be able to increase their input power by the throttled power value if necessary.

Apart from the fact that such a procedure wastes energy that can be generated from the wind, it also fails to take into account the fact that the power that is to be supplied to the wind power plant cannot be changed without putting a load on the wind power plant. Particularly rapid power changes can put a load on the wind power plant, which is unfavourable and can, for example, have an adverse effect on the service life of the wind power plant. In other words, such a load can lead to a reduction in the service life of the wind power plant. Although there are proposals by which such a reduction in service life can be estimated, this does not prevent such a reduction in service life.

In the priority application for the present application, the German Patent and Trademark Office has investigated the following prior art: DE 10 2017 112 936 A1, US 2017/0 328 342 A1, EP 2 354 541 A1, HEIER, Siegfried: Windfraftanlagen: Systemauslegung, Integration und Regelung, third revised and expanded edition, Wiesbaden: Vieweg+Teubner, 2003, pp. 431-434 and 456-462. - ISBN 978-3-663-07668-1, DE 102009 059669 A1, DE 102011 100981 A1, US 2009/0230681 A1 and DE 102016 120700 A1.

The invention is therefore based on the aim of solving at least one of the mentioned problems. In particular, a solution should be proposed which limits or reduces the load on the wind power installation arising from grid support requirements. At least one alternative solution to previously known solutions should be proposed.

According to the invention, a method according to claim 1 is proposed.

Accordingly, a method for controlling a wind power installation is proposed. Here, the starting point is a wind power installation, which is designed to feed electrical power into an electrical supply network and which comprises a tower with a nacelle rotatably arranged thereon. Furthermore, the wind power installation comprises an aerodynamic rotor that can be driven by the wind and a generator coupled to the aerodynamic rotor for generating electrical power from the wind. For this purpose, a power unit for controlling the generator is also provided in order to control an electrical power delivered by the generator.

The generator is driven, either directly or indirectly, by the aerodynamic rotor in order to generate electrical power from the wind. In addition, a power unit is provided for controlling the generator in order to control the electrical power delivered by the generator. In this way, the electrical power delivered by the generator can be controlled via the power unit. For this purpose, an active rectifier can be provided which rectifies the stator current of the generator, but at the same time controls it. By controlling the stator current, the wind power installation can also be controlled. At least this makes it possible to control the output power of the wind power installation.

In addition, a power supply unit is also provided to feed the electrical power delivered by the generator, or a part thereof, into the power supply network.

The present invention is based on these elements of a wind energy installation. On this basis, the process includes the following steps or stages.

The wind power plant is controlled in such a way that, in normal operation, a feed power is fed into the power supply grid based on the wind. In this sense, normal operation or operation is one in which no grid support or support requests are requested. The wind power plant therefore feeds in so-called grid parallel operation, in which as much power is fed as is possible due to the prevailing wind and of course the design of the wind power plant.

It is further proposed that the electrical feed power is changed depending on a grid state or a grid demand of the power supply network. For example, it may be provided that the fed-in or injected power is reduced as the grid frequency increases, at least as soon as the grid frequency has exceeded a predetermined limit value. In this case, the electrical feed power changes depending on a grid state. Insofar as this frequency-dependent power reduction is a requirement of the power supply network, the electrical feed power is also changed depending on a grid demand, at least indirectly.

However, it is also possible that a current and specific grid demand must be met, for example, the power supply network or its operator expressly requires that the power supplied be reduced by a certain percentage.

For this purpose, it is now also proposed that the change in the electrical feed-in power is carried out in such a way that a specifiable, in particular momentary, mechanical load limit of the wind energy installation is maintained. The wind energy installation does not therefore directly carry out the required change in the input power, either depending on a grid state or on a specific demand for power modification, but rather carries out the change in the electrical feed-in power. The change in the electrical feed-in power is carried out in such a way that the specifiable mechanical load limit of the wind energy installation is maintained. Such a mechanical load limit can also be or include a set of several individual load limits.

The underlying idea is that, for example, a sudden increase in the input power is only possible through a sudden increase in torque. It does not really matter whether the torque was increased directly or whether the power delivered or absorbed by the generator was suddenly increased, resulting in a sudden increase in torque.

In any case, the limitation of the specifiable mechanical power can be achieved in particular by ensuring that a corresponding power demand is not transmitted for implementation to the wind power installation, in particular to the generator, uncontrolled or unfiltered. Especially in the case of a desired power jump, i.e. one that is desired by the power supply network, this is transmitted somewhat weaker to the generator for implementation. For example, the use of a limit at an edge for changing the power can be considered, or such a power requirement can be managed by a dynamic filter. In a simple case, such a dynamic filter can be a filter with simple low-pass behavior, such as a first- or second-order delay element.

As a result, a power jump and the associated load on the wind power installation can be avoided by simply checking the filtering of the specified change value in the power.

It should be noted that the unhindered transmission of a sudden power change, to continue with this example, can cause a sudden change in the generator's torque and this leads directly to a mechanical load on the generator. Such a mechanical load on the generator can also be radiated onto the rotor blades of the wind power plant. Such a torque jump can also have an impact on the mounting of the generator on a machine stand of the wind power plant.

For such an undesirable load, which is now avoided according to the invention, other power changes are also taken into account in addition to the power jump mentioned by way of example, such as, for example, not sudden, but very rapid power changes.

In simulations, it is possible to record in advance which torque and/or power changes cause which mechanical loads or which mechanical load level. However, in-situ measurements can also be considered, in which rapid power and/or torque changes of this type are made. The resulting load can be recorded, for example, by means of strain gauges on the rotor blades or by means of strain gauges on other loaded elements, such as the rotor hub. It is preferably ensured that only a few such measurements are carried out and thus only a few excitations of the corresponding loads required for them. Alternatively, such a measurement can be carried out with very low load values and then a correspondingly high load can be calculated from this low load, in particular by extrapolation.

It should be noted that the proposal focuses on changing the electrical supply power. It is therefore checked to what extent the change in the electrical supply power leads to a mechanical load and the change in the electrical supply power is then carried out accordingly, in particular with such weak variations in time that the specifiable mechanical load limit is maintained. The specifiable mechanical load limit can also be referred to as a predetermined mechanical load limit.

In one embodiment, it is proposed to specify at least one limit gradient for the change in the supply power. Such a limit gradient is a maximum temporal change in terms of quantity of a power value, in particular of a power value of an electrical power generated by the generator. The limit gradient can also be a maximum temporal change in terms of quantity of a generator moment to be controlled. To illustrate graphically, such a limit gradient forms in time a rising edge, which must not be exceeded by the corresponding power or the corresponding generator moment, and a falling edge, which must not be exceeded by the corresponding power or the corresponding generator moment to be controlled. It is therefore proposed not to specify the corresponding power or the corresponding generator moment in terms of its range, but to limit it in terms of its range.

As long as the change in the feed-in power depending on the grid state or depending on the grid demand leads to a change in power or a change in the generator moment, which does not exceed the limit gradient in quantity, no change occurs. However, if the change in the feed-in power would require a larger change in quantity, the limit gradient would be reached and the change would therefore be limited. The result is that no changes that are too strong or too fast are transmitted to the generator and therefore no changes that are too strong or too fast are implemented. This ensures that a mechanical load limit is maintained for the wind power installation.

Through the preliminary investigations already mentioned, which can determine a relationship between power changes and resulting loads, the mechanical load can be determined and a corresponding limiting gradient selected based on the recorded relationship.

Preferably, the limiting gradients are variable. In particular, they can be specified depending on the situation. For example, a wind power plant operating at partial load, i.e. when the wind is so weak that the wind power plant cannot reach its rated power, may be subjected to a weaker mechanical load due to a change in the feed power than a wind power plant operating at full load, i.e. when operating in stronger winds.

Preferably, the limiting gradient can also be varied for the same process by allowing a strong increase from the start, but which can be reduced, for example, only a few seconds later, for example 3, 4 or 5 seconds later. This is based on the idea that a short, rapid initial increase in power leads to a mechanical load that remains permissible, while the additional mechanical load would be overcome if a correspondingly large change in the feed power were still permitted.

It is also possible that a mechanical load is caused solely by oscillation. Such an oscillation can also be prevented by specifying a corresponding limiting gradient. In this respect, it should be noted that a power change limitation or a generator moment change is a non-linear function. The effect therefore depends on the amplitude. Depending on the limited amplitude, this can lead to oscillations, which can conversely be prevented by specifying the limiting gradient appropriately. Here too, preliminary investigations such as simulations are necessary to check which limiting gradients can prevent or limit such or other oscillations.

In one embodiment, it is proposed to control the generator torque by means of a torque setpoint value, the torque setpoint value being passed through a filter element to reduce oscillation and/or to prevent oscillation excitation of the generator, the filter element being configured in particular as a low-pass filter and/or as a delay element, in particular as a first- or second-order linear delay element.

A special pre-filter is proposed for generator control. Such a filter element can also be called a pre-control. The filter element prevents a setpoint jump in the torque setpoint from occurring directly in the generator control. In this way, a jolt in the generator can be avoided, which could lead to oscillation. The filter element prevents such jolts and thus prevents such excitation of oscillations or can also serve to reduce the oscillations.

By using a low-pass filter, the higher frequencies are particularly removed from the torque setpoint. In particular, the use of a linear low-pass filter, such as a first- or second-order linear delay element, enables dynamic observation, in particular also observation in the frequency range. This makes it possible to take into account specific natural values or a resonance frequency of the generator.

The use of a limit gradient and a filter element, which can also be synonymously referred to as a filter, can also be combined. In particular, such a combination can be such that the generator power and/or torque are first limited by the limit gradient and the signal thus limited is then processed. The signal thus limited can already represent a limitation of a torque setpoint and can then be transmitted as such via the filter element. Alternatively, the limited signal, especially if it is a power, can first be converted into a torque setpoint and the resulting torque setpoint can be transmitted via the filter element.

According to the invention, it is provided that the change in the electrical supply power is controlled in such a way that after a generator torque exceeding a predetermined torque limit value in terms of quantity, another generator torque exceeding the predetermined torque limit value is suppressed for a predetermined recovery interval or is limited to the torque limit value. This means that an excessive generator torque is initially permitted. If a further generator torque exceeding the torque limit subsequently occurs, this is no longer permitted. Depending on the situation, this may mean that it is generally not permitted, but is preferably limited to the torque limit. This is preferably done for 5 to 30 seconds. Preferably, the generator torque exceeding the predetermined torque limit value is also permitted for a predetermined period of time and this period may correspond to the recovery period or interval.

However, it was recognised that the underlying problem may be that the generator and the mechanical structure behind it can oscillate due to several large generator moments in succession. In this respect, there is generally no problem that the generator moment is permanently too large. It should also be noted here that such a high generator moment, which can also be synonymously referred to as generator torque, is produced in particular by a change in power.

Such a high generator moment can occur in particular if impulse energy, i.e. kinetic energy, is to be extracted from the rotor of the wind power plant. If such a high generator moment occurs, this means that the generator is also braked considerably. If this high generator moment were to be maintained for a long period of time, for example for a minute, it could lead to such strong braking of the generator and thus the rotor of the wind power plant that it could come to a standstill. Such a situation is also unfavourable and generally undesirable, but a high mechanical load no longer occurs.

However, the present invention relates to the reduction or limitation of a mechanical load and, following the example mentioned, this can occur in particular by taking the kinetic energy from the rotor of the wind power installation in the short term and for a short period of time by means of a correspondingly high generator moment, for example for 5 seconds. This can be the case, for example, if the frequency in the power supply network varies and the wind power installation wants to counteract this by increasing the short-term power feed.

If the generator torque is very high for a short period of time, such as the 5 seconds mentioned as an example, it can be assumed that no additional power will be requested in the following 5 seconds due to the frequency oscillation in the power supply network and the generator torque will have fallen again accordingly. Also 5 seconds later, continuing with the example above, a high power demand can arise again, with a correspondingly high generator torque. This means that there are potentially strong torque changes every 5 seconds. Depending on the frequency of these strong torque changes, they can cause the generator or the rotor-generator system to oscillate. To prevent this, the recovery interval mentioned is provided. This prevents a rapid sequence of high generator torques.

In another embodiment, it is proposed that the change in the electrical supply power is controlled in such a way that in the event of a decreasing oscillation of the generator torque with a maximum amplitude exceeding the predetermined amplitude limit value, another generator torque pulse with at least half the amplitude of the amplitude limit value is prevented. Thus, if the generator torque oscillates, which may be accompanied by a mechanical oscillation of the generator and the rotor, further generator torque pulses are suppressed. If these generator torque pulses are small, in particular less than half the amplitude of the amplitude limit value, this suppression can be dispensed with.

In this way, it is possible to prevent a declining and therefore still existing generator torque oscillation from being re-excited. For this purpose, it is proposed that this suppression of such additional generator torque pulses is carried out until the declining oscillation has decayed to an amplitude that is below a predetermined amplitude drop value. This amplitude drop value is preferably chosen to be less than 25% of the amplitude limit value.

At most, an oscillation with an amplitude of one quarter of the limiting amplitude value still occurs, and with a value as small as one quarter, it can be assumed that the oscillation has essentially subsided.

Alternatively, a decay or ramp-down period can also be selected, so that further generator torque pulses with the corresponding level are only suppressed after a predetermined ramp-down period has elapsed. This ramp-down time is preferably in the range of 5 to 30 seconds. Here it was found that, depending on the generator, the generator oscillation had decreased, which can be assumed after 30 seconds even for generators with a low oscillation frequency. Of course, a different ramp-down time can also be selected depending on the generator.

According to one embodiment, it is proposed that a generator control circuit is formed for controlling the generator, which includes at least the generator and the power unit. It is further proposed that a control dynamics for the generator control circuit, in particular eigenvalues and/or pole positions, is specified, and the specification of the control dynamics, in particular the eigenvalues or the pole positions, is carried out in such a way that the specifiable mechanical load limit of the wind energy installation can be maintained.

When a generator control circuit configured in this way is used, the torque can be specified as a setpoint and thus constitute the input variable for the control circuit. From this value the current actual value is subtracted from the torque value and the resulting control difference is obtained via a controller whose dynamics can be specified or through which the control circuit dynamics can be specified.

The output of such a controller can then be a manipulated variable. The manipulated variable can be passed on to the power unit for implementation. The manipulated variable can be, for example, an adjustable excitation current if the generator is configured as an externally excited synchronous generator. Via this excitation current, the generator torque can be adjusted or at least fundamentally modified.

But this is only a particularly illustrative example. According to another example, the generator torque can be adjusted by means of an active rectifier. The active rectifier can do this by controlling the stator current delivered by the generator and from it the power delivered by the generator. This in turn allows the generator torque to be adjusted.

The generator control circuit can also be used to directly adjust the generator power, i.e. its output power. In this case, a setpoint value for the output power must be set. This can be compared with an actual value of the output power, i.e. the generator power, and the resulting control difference can be given via the controller, which calculates a manipulated variable from this and sends it to the power unit for implementation.

It was therefore recognised that such dynamics can be specified via this generator control circuit, which can also influence the mechanical load and thus avoid mechanical overload. In particular, by parameterising this generator control circuit, the generator control can be made so slow that excessive generator moments and thus excessive mechanical loads are avoided.

The use of such a generator control circuit can also be combined with the suggestion of the limit gradients and/or the suggestion of the pre-connected filter element. If necessary, the parameterization of the generator control circuit must be adapted accordingly.

In one embodiment, it is proposed that the generator control circuit comprises mechanical elements or mechanical properties are taken into account, namely the aerodynamic rotor, in particular its moment of inertia, and/or at least one natural frequency of the blade and also, or alternatively, the tower with the nacelle, in particular at least one natural frequency of an oscillation of the tower with the nacelle.

It is therefore proposed to take into account this dynamics, which results from the mechanical properties, in the generator control circuit. This consideration is especially reflected in the parameterization of the control circuit. In particular, it is known that both the aerodynamic rotor and the rotor blades as well as the interaction between the tower and the nacelle can respectively exhibit a corresponding eigenfrequency and/or complex conjugate eigenvalues. These properties can be known or determined by simulations. These properties can then flow into the generator control circuit, especially in the parameterization of the generator control circuit.

In one embodiment, it is proposed that a property or behaviour of the power supply network is included in the generator control circuit, in particular that a natural frequency and/or an oscillation of the power supply network is included. A property, in particular a natural frequency, of the power supply network is thus a general property which can, but does not necessarily, lead to an oscillation. If it causes an oscillation, the associated frequency is known. This frequency is also important for the question of its excitation and it is precisely for this reason that it is proposed to take it into account in the generator control circuit.

Additionally, or alternatively, the current behaviour, in particular a current oscillation of the power supply network, can be recorded and then taken into account directly in the control circuit. In this case, the control circuit could be designed adaptively to take into account such current behaviour, in particular a current frequency of an oscillation. Alternatively, the control circuit can be configured so robustly that it can cover a spectrum of possible frequencies. Such a spectrum can be the result of empirical values.

In one embodiment, it is proposed that a mechanical model of the wind power plant is taken into account when changing the electrical input power, in order to carry out the change in electrical input power in such a way that a specifiable, in particular momentary, mechanical load limit of the wind power plant can be maintained. It is particularly preferred that the mechanical model is contained in the generator control circuit or at least taken into account there.

Such a mechanical model modulates in particular the relationships between mechanical movements, mechanical deflections and mechanical forces, i.e. represents them. This preferably includes modulating a relationship between the generated generator moment, which therefore also acts on the rotor, and the resulting rotor movement, as well as other forces occurring on the rotor. It can therefore include an acceleration behaviour of the rotor as a function of such torque, including a resulting bending of the rotor blades, the resulting forces on the rotor blades and in particular on the pitch bearing to which the rotor blades are fixed in the rotor hub and possible oscillations occurring.

If, for example, the electrical feed power is to be increased, it can be determined how the generator torque will increase. This generator torque or its expected increase can then be an input value for the mechanical model and, based on this, it can be determined which mechanical loads are to be expected. These can then be compared with the specifiable mechanical load limit and, depending on this, the variation or change of the electrical feed power can be adjusted, i.e. reduced or slowed down, if necessary.

This consideration can be achieved by including the mechanical model in the generator control circuit. For example, a mechanical load recognized by the mechanical model can change a control gain in the generator control circuit by means of a control prescription. For this purpose, the mechanical model can be integrated directly into the generator control circuit. However, for example, the mechanical model can also be taken into account in the generator control circuit by adapting the input variable of the generator control circuit, i.e. the setpoint for the generator moment or the setpoint for the generator power to be adjusted, depending on the mechanical model.

In one embodiment, it is proposed that oscillation detection means be provided for detecting at least one oscillation of the wind energy installation, in particular for detecting mechanical oscillations and/or generator oscillations, where the at least one detected oscillation is used to effect the change in the electrical supply power such that the specifiable mechanical load limit of the wind energy installation can be maintained.

A variant proposed here is therefore that mechanical oscillations and/or generator oscillations are detected directly. The focus here is on mechanical oscillations of the wind power plant and/or generator oscillations. Mechanical oscillations of the wind power plant can also be rotor oscillations, especially in the direction of rotation. This can be due, for example, to the elasticity of the rotor blades. However, oscillations in the longitudinal direction of a rotor rotation axis and thus of the generator rotation axis are also taken into account. These oscillations can also be caused by power changes and thus by load changes.

It is also proposed to record generator oscillations. Such generator oscillations can also be mechanical oscillations. However, it is also possible to detect a torque oscillation, which can be detected electrically. However, such a torque oscillation regularly leads to a mechanical oscillation. In particular, it is proposed to use the method for a gearless wind power plant. In this case, the generator oscillations also act directly on the rotor, i.e. without the interposition of a gear, and the rotor oscillations also act on the generator.

An oscillation detection means can be, for example, an acceleration sensor, which can detect in particular, but not exclusively, oscillations of the rotor and thus of the nacelle of the wind energy installation in the longitudinal direction of the rotor axis. Strain gauges can also be considered which can detect oscillations due to stresses in the tower of the wind energy installation and/or which, when appropriately installed, can detect oscillations of the rotor blades if, for example, they are arranged in a root region of the rotor blades. An oscillation measurement can also be recorded via a rotor position sensor, if a temporal development of the rotor position recorded in this way is evaluated, which can also be referred to as the rotor rotation position.

Generator torque oscillations can be derived from the control of the wind power installation, which regularly knows the current output power of the generator. Torque oscillations can also be detected by a specific current sensor as an oscillation detection means. This is just another example of an oscillation detection means. Another example that could be considered are optical sensors that can record element movements.

In one embodiment, it is proposed that, for controlling the generator, in particular for controlling by means of a torque setpoint value, a limiting filter is provided for limiting a control signal, in particular the torque setpoint value, to a predetermined limit amplitude in a specific frequency range.

The limiting amplitude is preferably specified as a frequency-dependent amplitude variation curve. The underlying idea is that the relationships between the generator torque and the resulting mechanical loads are already known. These relationships can be recorded in advance by means of measurements or simulations. The predetermined frequency range including the associated limiting amplitude, which can thus be predetermined, can also be defined and specified accordingly. Through this limiting filter, compliance with the specifiable mechanical load limit can then be achieved easily and particularly quickly. In particular, this proposal does not require any traceability of the measurements.

Especially in preliminary investigations, whether in a real system or by means of simulations, a frequency dependence can also be fundamentally and quantitatively recognized and recorded. The limiting amplitude can therefore vary depending on the frequency. A frequency-dependent amplitude variation curve can especially refer to the use of, for example, a step signal as a torque setpoint. According to Fourier theory, such a step signal consists of different frequency components and this is exactly what can be taken into account when specifying a frequency-dependent amplitude curve. Such a limiting amplitude can be considered to be configured as a frequency-dependent corresponding function or as a frequency-dependent limiting system. A frequency-dependent corresponding filter is taken into account here.

The wind power plant preferably has a synchronous generator and in particular is designed without gears. It is also provided that the power unit has a rectifier and a boost converter, or that it has a controlled rectifier. If it has a controlled rectifier, the boost converter is not necessary.

For this use of a synchronous generator, it is now envisaged that either the boost converter or the controlled rectifier will be used to control the generator to control the electrical power delivered by the generator or to control the generator torque. The stator current of the generator can be controlled by both the boost converter and the controlled rectifier. This stator current is a delivery current of the synchronous generator.

By controlling this stator current, the output power of the synchronous generator can be controlled. With suitable conversion and taking into account the rotational speed of the generator rotor, a torque can also be derived from the stator current or a generator torque can be set via the stator current. In this way, the generator moment and thus also the torque acting on the rotor can be specified as desired.

In the case of a gearless wind power plant, which is predominantly used, the rotor torque can be specified directly. Especially if the rotor moment is a critical quantity with respect to the specifiable mechanical load limit, a corresponding load can be directly influenced by this control of the synchronous generator and, if necessary, adjusted and limited. Even if other or additional elements are relevant to the specifiable mechanical load limit, such as a bending and/or oscillation of the rotor blades, this can also be easily influenced by controlling the electrical power delivered by the generator or the generator moment via the aforementioned power unit.

The synchronous generator is preferably designed as an externally excited synchronous generator and the power unit then comprises an excitation controller, in particular a direct current controller, for thereby controlling an excitation current of the synchronous generator. This makes it possible to control the excitation of the synchronous generator and thus to easily control the generator torque. This can also be used to control the electrical power delivered by the generator. In this way, the power unit has a good and in particular additional possibility of adjusting the generator power and/or torque and thus influencing the mechanical load.

According to the invention, a wind power plant is also proposed, which is designed to feed electrical energy into an electrical supply network. This comprises:

- a tower with a gondola rotating on it,

- an aerodynamic rotor that can be driven by the wind,

- a generator coupled to the aerodynamic rotor to generate electrical power from the wind,

- a power unit for controlling the generator to control an electric power delivered by the generator and/or to control a generator torque and

- a power supply unit for feeding the electrical power delivered by the generator, or part thereof, into the electrical supply network,

- a control unit for controlling the wind power installation so that, in normal operation, an electrical power supply is fed into the power supply network based on the wind, where the control unit is prepared for,

- control a change in the electrical power supply depending on a network status and/or a network demand of the electrical supply network, where

- the change in the electrical supply power is carried out in such a way that a specifiable mechanical load limit, in particular momentary, of the wind energy installation is maintained.

The wind power plant is therefore configured as already explained above in connection with the method according to the invention for controlling a wind power plant.

The control unit of the wind power plant can be configured in particular as a processor and can be coupled in particular to the power unit and the supply unit. In this respect, the control unit preferably controls both the power unit and the supply unit. However, it is also possible at least in part that the supply unit is controlled indirectly by the power unit.

Such a control may be configured such that the power unit also controls a power supply and, over time, a power supply to the power supply unit by controlling the delivery of electrical power by the generator or indirectly by controlling the generator moment. A part of the control of the power supply unit may then be configured such that the power supply unit controls the feed to the electrical supply network depending on the power or energy it receives from the power unit or by controlling the power unit.

The control unit can also be connected to a detection unit for detecting at least one network status. In particular, the voltage in the power supply network or a representative voltage at the output of the supply unit and also the current and/or power supplied can be recorded here.

The detection of the voltage of the power supply network includes not only a voltage amplitude but also a frequency of the electrical voltage. In addition, a phase position is detected, in particular a phase position of the electrical voltage with respect to the supplied electrical current. A proportion of the supplied reactive power can also be derived from this. From these values, in particular from the recorded grid frequency and/or from a change in the grid frequency, the need for a change in the power to be supplied to the power supply network can also be deduced.

This need for change can then be evaluated in the control unit and, based on this, the generator control can be controlled again, namely by controlling the power unit. The control unit can receive information about the status of the grid and also from the supply unit if it records grid variables or grid states, or parts thereof.

The control unit can also contain the specifiable mechanical load limit. This can therefore be specified in the control unit. If this is specified based on a specification and/or based on input variables, this specification can also be carried out in the control unit. The mechanical load limit can also be calculated or determined in another way there. For the absolute values of the specifiable mechanical load limit, it is also possible to store them in advance in the control unit, especially in the factory. However, it is also possible that these are updated occasionally.

In one embodiment, it is provided that the wind energy installation, in particular the control unit, is configured to carry out a method for controlling a wind energy installation according to at least one embodiment described above.

The control unit can be configured accordingly for this purpose. Such a configuration can also include the above-mentioned connections between the control unit and the power unit as well as the supply unit. This preparation of the control unit for carrying out the above-mentioned procedure can also include the connection of a measuring unit for recording the network states, in particular the electrical values of the power supply network.

A mechanical model of the wind power plant can be used to estimate mechanical loads, in particular to estimate them in advance. This mechanical model can also be configured and used as explained above in connection with embodiments of the method for controlling a wind power plant.

According to the invention, a wind farm with a plurality of wind energy installations is also proposed. It is provided that the wind energy installations, at least a part of them, are designed according to at least one embodiment of a wind energy installation described above.

What is particularly important here is that the wind power installations together feed into the power supply network at a grid connection point and thus change this total electrical feed-in power depending on the grid status and/or grid demands, whereby a change in the electrical feed-in power of each individual wind power installation is controlled in such a way that a specifiable mechanical load limit is maintained for each individual wind power installation. This enables better monitoring of the total power fed into the grid connection point depending on the grid status or grid demand.

In one embodiment, it is proposed that the wind farm is connected to the power supply grid at a grid connection point in order to feed a wind farm electrical power into the power supply grid. The wind farm electrical power is essentially the sum of all the electrical power supplied by the wind energy installations of the wind farm at any given time.

In addition, a central wind farm control system is provided for the wind farm to coordinate the wind energy installations so that the electrical power of the wind farm is fed into the power supply network at the point of grid connection, in particular taking into account the respective specifiable load limit of each wind energy installation. The central wind farm control system thus coordinates the wind energy installations with regard to their electrical feed-in power.

For this purpose, the central wind farm control can assign each wind power installation an individual setpoint for the feed-in power. The wind power installation then sets the feed-in power accordingly and the sum of all these feed-in powers is essentially the wind farm power. However, if a change in the feed-in power is required or if such a change is announced, each wind power installation can send a signal to the central wind farm control to indicate to the central wind farm control a limit to the possible change in feed-in power.

Depending on this, the central wind farm control can then adjust the distribution of wind farm power between the wind power installations, for example by having a wind power installation that has not yet reached a specifiable mechanical load limit take over part of the power that another wind power installation cannot deliver at that time due to a mechanical load limit.

It is also possible to consider that if a desired change in wind farm power cannot be achieved due to the specifiable mechanical load limits of all wind energy installations, then a new wind farm power is specified that can be achieved.

Furthermore, it is envisaged that, according to one embodiment, it is proposed that the central fleet control transmits information to a network operator operating the power supply network about the extent to which a change in the fleet's electrical power can be implemented. The power supply network or its network operator can then adapt to this situation.

The invention is explained in more detail below using exemplary embodiments with reference to the attached figures.

Figure 1 shows a wind power installation in a perspective view.

Figure 2 shows a wind farm in schematic representation.

Figure 3 shows a generator control in a schematic representation.

Figure 1 shows a wind power installation 100 with a tower 102 and a nacelle 104. A rotor 106 with three rotor blades 108 and a spinner 110 is arranged in the nacelle 104. During operation, the wind causes the rotor 106 to rotate and thus drives a generator in the nacelle 104.

Furthermore, a power supply unit 101 is provided for feeding electrical power delivered by the generator into a power supply network 120. For this purpose, the power supply unit outputs a three-phase alternating current, which can be fed into the power grid 120 via a grid transformer 116 at the common grid connection point 118.

Furthermore, a current sensor 103 and a voltage sensor 105 are shown in Figure 1, which together can also form a measuring device. The current and voltage that can be detected in this way can be used as an input signal for the supply unit 101. This means that grid states such as the grid frequency or grid voltage can also be recorded. In order to detect the grid voltage, the transmission behaviour of the grid transformer 116 can be taken into account. Via the current sensor 103 and the voltage sensor 105, it is also possible to detect the phase position of the current and voltage relative to each other and thus also to detect the fed-in active power and the fed-in reactive power or, with them, also to detect a power factor. These quantities form grid states. These values can therefore also be used when feeding in and also when taking into account specifiable mechanical load limits.

Figure 2 shows a wind farm 112 with, for example, three wind power installations 100, which may be the same or different. The three wind power installations 100 are therefore representative of basically any number of wind power installations in a wind farm 112. The wind power installations 100 make their power, in particular the generated current, available via a power park network 114. The currents or powers generated in each case by the individual wind power installations 100 are added together and a transformer 116 is usually provided, which transforms the voltage in the park and then feeds it into the supply network 120 at the feed-in point 118, which is also generally referred to as PCC. For example, the park network 114 can be designed differently, for example by also having a transformer at the output of each wind power installation 100, to name just another exemplary embodiment.

The wind farm 112 also has a central wind farm control 130. The wind energy installations 100 can be coordinated with this central wind farm control 130. For this purpose, there is communication between the central wind farm control 130 and the wind energy installations 100. This communication can be wired or wireless. For the sake of clarity, no communication connections between the central wind farm control 130 and the wind energy installations 100 are shown.

Communication between the central wind farm control 130 and a grid operator is also considered. Such communication may take place with a grid control centre 132 of the grid operator and this is indicated in Figure 2. The grid operator may also request support power and the central wind farm control may inform the grid operator to what extent and in what manner the request can be met. A restriction to maintain a specifiable mechanical load limit may be taken into account here. In this way, the grid operator may receive information on to what extent the wind farm 112 can cover its request, even taking into account such a mechanical load limitation.

A control of a synchronous generator 302 is shown schematically in Fig. 3. In the synchronous generator, the rotor 304 and the stator 306 are each configured as annular areas. Fig. 3 shows them in an indicated sectional view, so that they are shown as shaded areas. These shaded areas are essentially the magnetically effective areas of the rotor 304 or the stator 306.

The rotor 304 is shown here as an internally arranged rotor, so that the synchronous generator 302 is designed in this example as an internal rotor and as an annular generator. The rotor 304 is firmly connected to an indicated aerodynamic rotor 106. This aerodynamic rotor 106 thus corresponds to the aerodynamic rotor 106 according to FIG. 1 and has the correspondingly indicated rotor blades 108.

For illustrative purposes only, only two rotor blades 108 are shown in Figure 3. For the sake of simplicity, the same reference numerals have been chosen here as in Figure 1 to indicate that these may also be the same elements as in Figure 1. The same applies to the other elements in Figure 3, which have the same reference numerals as in Figure 1 and/or Figure 2. All of these elements may correspond to the corresponding elements in Figures 1 or 2 or both, even if a different form of representation has been chosen.

The synchronous generator 302 can thus be arranged in the nacelle 104 of the wind power plant 100 according to FIG. 1. In the example shown, the stator 306 of the synchronous generator 302 is configured in six phases, i.e. with two three-phase systems offset from each other by 30 degrees. The stator 306 is attached to a support frame 308, which is merely indicated. By means of this support frame 308, the synchronous generator 302 is thus fixed in a nacelle such as that of the nacelle 104 in FIG. 1, i.e. on a machine stand.

The six-phase stator current Is is then supplied to an active rectifier 310. The active rectifier 310 rectifies this six-phase stator current Is and generates a direct current with direct voltage and transmits it to the direct voltage intermediate circuit 312. The active rectifier 310 can also specifically control the stator current I<s> and thus also control a torque of the synchronous generator 302. For this purpose, the active rectifier 310 can be provided with a power setpoint value Ps and optionally a reactive power setpoint value Q<s>, not shown in FIG.

The power setpoint values Ps and, if applicable, Qs can be specified by a control unit 314, for example. Such a power setpoint value Ps, which is specified by the control unit 314, can be specified, for example, depending on a rotational speed of the aerodynamic rotor 106 according to a rotational speed-power curve. The control unit 314 can calculate this accordingly. Only to simplify the illustration, an input of a detected rotational speed n is not shown in the control unit 314. Otherwise, the schematically represented control unit 314 can anyway carry out any control of the wind energy installation or can carry out a large part of the control of the wind energy installation and then have such a rotational speed value available anyway.

In this way, an operating point of the wind power installation is set by the power setpoint Ps. In a special situation, which will be described below, this set power can be changed at least briefly by a power differential APf. In this respect, APf is shown in Figure 3 as an additional input variable for the active rectifier 310.

In any case, the power or energy that the active rectifier 310 has introduced into the intermediate direct voltage circuit 312 is converted by the supply unit 101 into a three-phase alternating current with a three-phase alternating voltage and is finally fed into the power supply network 120 at the common network connection 118.

The power supply unit 101 shown schematically can use the measured currents and voltages, especially those recorded with the current sensor 103 and the voltage sensor 105, to record network states of the power supply network 120. One possibility is to record a network frequency fN as the network state.

It can now be provided that, depending on the detected mains frequency, a backup power is fed into the power supply network, namely in addition to the current power, in particular in addition to the predetermined power P<s> of the operating point. What is particularly important here is that, in the event of short-term drops in the mains frequency fN, the backup power should be fed into the power supply network quickly and only for a short period of time. A short period of time can in particular be in the range of 5 to 30 seconds. Such a backup power can be in the range of 5 to 20 percent of the current output power of the synchronous generator 302, i.e. in the range of 5 to 20 percent of the power P<s>.

This additional support power can be generated by the synchronous generator by electrically braking it, whereby the kinetic energy is converted into electrical power. For this purpose, the active rectifier 310 can correspondingly increase the stator current I<s>. If necessary, an excitation current can be set. This also increases the generator torque, which causes said electrical braking of the rotor and thus an increase in the generated power. In particular, the aerodynamic rotor 106 is braked, but also the rotor 304, which can also be called an electrodynamic rotor.

Its kinetic energy is therefore converted.

It has now been recognised that such support can be very useful, but it can also represent a high mechanical load for the wind power installation. Consequently, it is proposed to change the electrical power, specifically to increase the electrical power delivered by the generator, in order to manage the differential power APf in such a way that a specifiable mechanical load limit of the wind power installation is maintained. One way of implementing this is explained in Figure 3.

The power supply unit 101 therefore outputs the grid frequency fN and passes it on to the power shifting block 320. It is possible that this has implemented a function which determines a frequency-dependent power shift f, which is given here as the grid frequency fN. For simplicity, it can be assumed that the power shifting block 320 also knows, i.e. has implemented or stored, the nominal grid frequency, i.e. the frequency which the power supply grid should have, i.e. typically 50 Hz or 60 Hz. The implemented function will typically be as follows: If the frequency corresponds to the nominal frequency, the required power shift is the value 0.

In the example explained, however, it is assumed that the grid frequency fN has clearly fallen below the nominal frequency. Depending on this, the power change block 320 then calculates a corresponding power differential setpoint value AP<s>. The output power of the synchronous generator 302 should be increased by this power differential setpoint value APs. The underlying idea is that the power losses are negligible and that this increased power is also fed in, so that the electrical supply power is modified in the same way.

In order to comply with the specifiable mechanical load limits of the wind power installation, this power change setpoint APs is not provided directly as a setpoint to the active rectifier 310, but is first passed through a filter element 322.

There are several ways in which this filter element 322 can be designed. Two of these options are indicated graphically in Figure 3. The left variant is shown in a solid block and the right variant in a dashed area. This is intended to indicate that these variants may be alternatives.

The variant of the filter element 322 indicated on the left is designed as a low-pass filter. Low frequencies are allowed to pass and higher frequencies are attenuated more the higher they are. In the case of the power change setpoint APs, it is taken into account that this setpoint can be generated by the power change block 320 when the mains frequency fN changes very quickly as a step-adjusted setpoint or a suddenly increasing setpoint. In this case, the rising edge of such a step value corresponds to a high-frequency signal or high-frequency component of a signal and the indicated low-pass filter would attenuate such a sharp edge accordingly.

The variant on the right specifies a maximum gradient, specifically for the amount of change, so that a rising positive edge and a falling negative edge form the corresponding limits. The setpoint value entered in the filter block 322 is therefore limited to these edges. Incidentally, in addition to these two variants shown, other variants of the low-pass filter and the limited gradients can of course exist. A combination can also be considered.

The output of the filter element 322 is a filtered power change APf, which is now fed into the active rectifier 310 as a setpoint. The active rectifier 310 is not supplied with a strong jump-shaped signal via the filter element 322, so that the synchronous generator 302 can no longer be controlled as strongly.

However, it is also taken into account that the filter element 322 is time-variable or time-variably controlled in order to change the respective filter function. This applies both to the low-pass filter variant and to the gradient limiting variant, i.e. to other variants.

With such a time-dependent or time-dependent control, it can be specifically foreseen and implemented that account is taken of how often the wind power installation, in particular the synchronous generator 302, has already had to bear a strong load due to a sudden demand for a rapid increase in power. It has been recognized that a sudden strong increase in power, which is accompanied by a corresponding increase in the generator moment, does not directly damage the wind power installation, but in the case of continuous load it can be critical and can damage the wind power installation.

A continuous load is in particular one in which such power increases are requested in short intervals, such as minute intervals or intervals of 5 to 10 seconds. In this case, it is possible that the first such power increase is passed on unfiltered to the active rectifier 310 and thus, as a result, to the synchronous generator 302. However, if another such request for a sudden power increase arrives within a short time, then, or only from a predetermined number within a predetermined time period, the filter element 322 can develop its effect in such a way that said power jump is no longer permitted to pass through.

In particular it was recognized here that many such power jumps in rapid succession also create the risk that the synchronous generator 302 or the rotor 106 will go into oscillation. This can be prevented by the filter element 322, where a first sudden change in power can be transmitted unfiltered.

Another variant is shown in dashed lines in Fig. 3, whereby a power change is indicated by a grid operator instead of a measured grid state. This is indicated by control centre 132, which may correspond to control centre 132 in Fig. 2. This control centre may, for example, demand a power change APp of a wind farm power. The grid control centre may therefore demand that the total wind farm power supplied by a wind farm, such as wind farm 112 in Fig. 2, be changed by the amount given by this change in wind farm power APp.

Such a request for a changed park power can be sent to a central park control 130, as shown in Figure 2. The central park control 130 can then convert and output this park power setpoint value into a setpoint value for a changed installation power. The central park control 130 therefore generates a power change setpoint value APs and delivers it to the filter element 322. This then replaces the specification of a power change setpoint value APs, which was generated by the power change block 320 according to the first variant. Otherwise, further processing of this power setpoint value can be carried out in the filter element 322 as explained above.

A solution is therefore proposed which creates a change in the feed-in power taking into account the mechanical load. The change in the fed-in power can be due to a grid state, including a grid oscillation, which can be detected. The grid state, which in principle can also include several elements and is therefore also synonymous with several grid states, can be recorded in particular by the wind power installation or a park control, or it can be entered via an external interface, for example by a grid operator who can request a change in power. These three options can also be referred to as 3 levels.

In particular, a solution is proposed to access the rotational energy of the rotor of the wind power plant to improve the grid properties.

The solution is therefore to use rotating storage, especially for local system services. This can include the provision of control power, a flywheel simulation, voltage printing and optimized power gradient limiting.

It was recognized that an active rectifier allows very high active power gradients in the generator and can therefore realize corresponding torque gradients. For this purpose, a suitable limitation is proposed to limit the mechanical stress. Thus, a reduction or limitation of the loads on the mechanical structure in case of grid-related power gradients is proposed.

Preferably, a dynamic limitation of the active power gradients is provided as a function of the load on the mechanical structure.

In particular, it was recognised that access to the rotor's rotational energy can be achieved via an active rectifier, which enables high torque gradients on the rotor shaft. This means that high loads on the mechanical structure are possible.

New system services can be used to link the mechanical oscillation system of a wind power plant with the oscillation systems of the grid. This is counteracted by the proposed solution.

In particular, the following is suggested:

Limiting torque gradients or the torque curve in order to avoid mechanical stresses or to exceed maximum loads. In particular, a gradient limitation and/or a shifting of an excitation spectrum by equalizing the torque curve, for example by means of a low-pass filter, in particular based on a first- or second-order delay element (PT1/PT2), is proposed.

One suggestion is to specify definitions of dead times that will be maintained after sudden increases in torque. A variant is to wait for the mechanical oscillation to subside.

Another basic approach is to avoid mechanical oscillations. To do this, it can be suggested to consider the resonance frequencies in the mechanical system when controlling the generator torque.

Memorization of the pole positions in the control used is also taken into account, according to which a distance between the pole positions in the complex plane with respect to the imaginary axis is adjusted or increased.

A representation of the mechanical model is preferably carried out in the control.

One variant proposes detecting the oscillations and the reaction of the generator control in order to be able to react technically to such oscillations.

It is also suggested to avoid any excitation by specifying a specific frequency range as a limiting curve. This can also depend on a predetermined amplitude or the amplitude is specified as a limiting curve. Advantages of the proposed solutions include avoiding/reducing mechanical stress while improving the network properties compared to solutions that do not take mechanical stress into account.

It is also possible to decouple the oscillation systems from the power grid on the one hand and from the wind power plant on the other. This can be achieved by means of an adapted generator control that takes these two oscillation systems into account.

In particular, it has been recognized that when the generator moment changes, the mechanical structure may suffer special loads in the following two ways.

In the first type of loading, an absolute single load occurs immediately at the torque jump. This can influence the bending of the wind power plant tower, the bending of the rotor blades, as well as the maximum loads and service life.

A second type of load results from a cyclic variation of the torque. This can excite a resonance in the mechanical system.

For this purpose, the resonance frequencies of the mechanical system must be taken into account. A first oscillation of the tower may be in the range of 0.25 Hz. A second oscillation of the tower may be in the range of 1 - 3 Hz. A first blade frequency in the flapping direction may be in the range of 0.55 Hz, and a first blade frequency in the rotation direction may be in the range of 0.75-0.9 Hz.

For this purpose, it is proposed to take into account the frequencies of the electricity supply network. It was recognized that the so-called interregional oscillations, i.e. power oscillations between sections of the network, can fluctuate between 0.2 and 0.8 Hz.

So-called power system oscillations (“PSO”), i.e. local power oscillations, can have frequencies starting from 1 Hz. Furthermore, so-called subsynchronous resonances (SSR), i.e. voltage oscillations with frequencies below the grid frequency, can occur especially in the range of 15 Hz.

Claims (14)

1. A method for controlling a wind power installation (100) to feed electrical power to an electrical supply network (120), and the wind power installation (100) comprises - a tower (102) with a gondola (104) rotatably arranged thereon, - an aerodynamic rotor (106), which can be driven by the wind, - a generator (302), which is coupled to the aerodynamic rotor (106) to generate electrical power from the wind, - a power unit (310) for controlling the generator (302) to control an electric power delivered by the generator (302) and/or to control a torque of the generator and - a power supply unit (101) for feeding the electrical power delivered by the generator (302), or part thereof, to the electrical supply network (120), and the procedure comprises the steps of - controlling the wind power installation (100) so that, in normal operation, an electrical power supply is fed to the power supply network (120) based on the wind, - changing the electrical power supply depending on a network status (fN) and/or a network demand (AP<s>) of the electrical supply network (120), where - the change in the electrical supply power is carried out in such a way that a specifiable mechanical load limit, in particular momentary, of the wind energy installation (100) is maintained, characterized by The change in the electrical power supply is controlled so that - following a generator torque exceeding a predetermined torque limit value in terms of quantity, a further generator torque exceeding the predetermined torque limit value is suppressed for a predetermined recovery interval or is limited to the torque limit value, in particular for 5 to 30 seconds, and/or - in the case of a decreasing oscillation of the generator moment with a maximum amplitude exceeding a predetermined amplitude limit value, a further generator torque pulse with at least half the amplitude of the amplitude limit value is prevented, - until the decaying oscillation has decayed to an amplitude which is below a predetermined amplitude decay value, which is chosen in particular to be less than 25% of the amplitude limit value, or - until a predetermined decay time has elapsed, which is in particular in the range of 5 to 30 seconds. 2. The method according to claim 1, characterized in that for changing the feed power at least one limit gradient is specified, where the limit gradient - defines a maximum change, in terms of quantity, over time, of a power value, in particular for the electrical power generated by the generator (302), or - defines a maximum change, in terms of quantity, over time, of a generator moment to be controlled. 3. The method according to any of claims 1 and 2, characterized in that a generator moment of the generator (302) is controlled by a torque setpoint value, where the torque setpoint value is passed through a filter element (322), for oscillation reduction and/or to prevent oscillation excitation of the generator (302), where the filter element (322) is configured in particular as a low-pass filter and/or as a delay element, in particular as a first- or second-order linear delay element. 4. Method according to one of the preceding claims. characterized in that - a generator control circuit, comprising at least the generator (302) and the power unit (310), is formed to control the generator (302), - a control dynamics, in particular eigenvalues and/or pole positions, is specified for the generator control circuit, and - the specification of the control dynamics, in particular of the eigenvalues or pole positions, is carried out in such a way that the specifiable mechanical load limit of the wind energy installation can be maintained. 5. Method according to one of the preceding claims. characterized in that in a, or in the, generator control circuit mechanical elements are included or mechanical properties are taken into account, from the list comprising: - the aerodynamic rotor (106), in particular its moment of inertia, and/or at least one natural frequency of the blade, and - the tower (102) with the nacelle (104), in particular at least one natural frequency of an oscillation of the tower (102) with the nacelle (104). 6. Method according to one of the preceding claims. characterized in that In one or the generator control circuit, a property or behaviour of the power supply network (120), in particular a natural frequency and/or an oscillation of the power supply network (120), is included. 7. Method according to one of the preceding claims. characterized in that - when changing the electrical supply power, a mechanical model of the wind power installation (100) is taken into account, in order to carry out the change of the electrical supply power in such a way that a specifiable, in particular momentary, mechanical load limit of the wind power installation (100) can be maintained, in particular in that - the mechanical model is contained or taken into account in one, or the generator control circuit. 8. Method according to one of the preceding claims. characterized in that - an oscillation detection means is provided, for detecting at least one oscillation of the wind power installation (100), particularly for detecting mechanical oscillations and/or oscillations of the generator (302), where - the at least one detected oscillation is used to change the electrical power supply so that the specifiable mechanical load limit of the wind energy installation (100) can be maintained. 9. Method according to one of the preceding claims. characterized in that - a limiting filter (322) is provided for controlling the generator (302), in particular by means of a torque setpoint, to limit a control signal, in particular the torque setpoint, to a predetermined limit amplitude in a specific frequency range, preferably - the limiting amplitude is specified as a frequency-dependent amplitude variation curve. 10. Method according to one of the preceding claims. characterized in that - the wind power installation (100) has a synchronous generator (302) and - the power unit (310) has a rectifier and a boost converter or a controlled rectifier (310), and - the boost converter or the controlled rectifier (310) is used to control the generator (302) to control the electrical power delivered by the generator (302) and/or to control the generator torque, where preferably - the synchronous generator (302) is configured as a separately excited synchronous generator and the power unit comprises an excitation controller, in particular a direct current controller and thereby controls an excitation current of the synchronous generator (302). 11. A wind power installation (100) for supplying electrical energy to an electrical supply network (120), comprising: - a tower (102) with a gondola (104) rotatably arranged thereon, - an aerodynamic rotor (106), which can be driven by the wind, - a generator (302), which is coupled to the aerodynamic rotor (106) to generate electrical power from the wind, - a power unit (310) for controlling the generator (302) to control an electric power delivered by the generator (302) and/or to control a generator torque and - a power supply unit (101) for feeding the electrical power delivered by the generator (302), or part thereof, to the electrical supply network (120), - a control unit (314) for controlling the wind power installation (100) such that, in normal operation, an electrical power supply is fed to the power supply network (120) based on the wind, where the control unit (314) is configured to - controlling a change in the electrical power supply depending on a network status and/or a network demand of the electrical supply network (120), where - the change in the electrical supply power is carried out in such a way that a specifiable mechanical load limit, in particular momentary, of the wind energy installation (100) is maintained, where The change in the electrical power supply is controlled so that - following a generator torque exceeding a predetermined torque limit value in terms of quantity, a further generator torque exceeding the predetermined torque limit value is suppressed for a predetermined recovery interval or is limited to the torque limit value, in particular for 5 to 30 seconds, and/or - in the case of a decreasing generator torque oscillation with a maximum amplitude exceeding a predetermined amplitude limit value, a further generator torque pulse with at least half the amplitude of the amplitude limit value is prevented, - until the decaying oscillation has decayed to an amplitude which is below a predetermined amplitude decay value, which is chosen in particular to be less than 25% of the amplitude limit value, or - until a predetermined decay time has elapsed, which is in particular in the range of 5 to 30 seconds. 12. The wind power installation (100) according to claim 11, characterized in that The wind energy installation (100), in particular the control unit (314), is designed for carrying out a method according to one of claims 1 to 10, in particular a mechanical model of the wind energy installation (100) being implemented in the wind energy installation (100), in particular in the control unit (314). 13. A wind farm (112) with a plurality of wind energy installations (100) according to claim 11 or 12. 14. The wind farm according to claim 13, characterized in that - the wind farm (112) is connected to the power supply network (120) at a grid connection point (118), to feed a wind farm's electrical power to the power supply network (120), - a central wind farm control (130) is provided for coordinating the wind energy installations (100) such that the wind farm's electrical power is fed into the power supply network (120) at the grid connection point (118), in particular while taking into account the respective specifiable load limit of each wind energy installation (100).